U.S. patent number 6,550,942 [Application Number 09/684,318] was granted by the patent office on 2003-04-22 for linear illumination sources and systems.
This patent grant is currently assigned to AlliedSignal Inc.. Invention is credited to Karl W. Beeson, Jerry Wayne Kuper, Hefen Lin, Michael James McFarland, Lawrence Wayne Shacklette, John Colvin Wilson, Scott M. Zimmerman, Han Zou.
United States Patent |
6,550,942 |
Zou , et al. |
April 22, 2003 |
Linear illumination sources and systems
Abstract
Improved linear illumination sources are disclosed which utilize
external, highly reflective enclosures containing one or more
linear openings and thereby achieve improved source efficiency,
output irradiance and/or output radiance. Such improved
illumination sources may be combined with additional optical
elements to produce more complex illumination systems.
Inventors: |
Zou; Han (Windsor, NJ),
Zimmerman; Scott M. (Basking Ridge, NJ), Wilson; John
Colvin (Wayne, NJ), Beeson; Karl W. (Princeton, NJ),
McFarland; Michael James (Washington, NJ), Lin; Hefen
(Cupertino, CA), Kuper; Jerry Wayne (Martinsville, NJ),
Shacklette; Lawrence Wayne (Maplewood, NJ) |
Assignee: |
AlliedSignal Inc. (Morristown,
NJ)
|
Family
ID: |
22036577 |
Appl.
No.: |
09/684,318 |
Filed: |
October 6, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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061562 |
Apr 16, 1998 |
6186649 |
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Current U.S.
Class: |
362/347; 362/260;
362/217.07 |
Current CPC
Class: |
G02B
6/001 (20130101); G03B 27/542 (20130101); F21V
7/005 (20130101); G01N 21/8806 (20130101); G02B
6/003 (20130101); G02B 6/0031 (20130101) |
Current International
Class: |
F21V
8/00 (20060101); F21V 7/00 (20060101); G03B
27/54 (20060101); F21V 007/00 () |
Field of
Search: |
;313/488,489
;362/347,260,217,341,31,26 ;349/65,70 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1533870 |
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Nov 1978 |
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GB |
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2020000 |
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Nov 1979 |
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GB |
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2255551 |
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Nov 1992 |
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GB |
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6-186433 |
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Aug 1994 |
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JP |
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Primary Examiner: O'Shea; Sandra
Assistant Examiner: Truong; Bao
Attorney, Agent or Firm: Roberts & Mercanti, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a division of U.S. patent application Ser. No.
09/061,562 filed Apr. 16, 1998 which is incorporated herein by
reference now U.S. Pat. No. 6,186,649.
Claims
We claim:
1. A linear illumination source comprising: (a) a linear light
source having a width w.sub.1 in a direction perpendicular to the
long axis of the linear light source; and (b) an external
reflective enclosure partially surrounding the linear light source,
wherein the external reflective enclosure has a maximum inside
width w.sub.2, and wherein the external reflective enclosure has at
least one linear opening of maximum width w.sub.3 such that
(0.03)(w.sub.2)<w.sub.3 <(0.75)(w.sub.2), wherein the
enclosure has an inside surface which comprises a reflective
material; and (c) at least one optical element in close proximity
to at least one linear opening; said optical element having a
planar light input end juxtaposed to said aperture, opposing
tapered walls extending away from the light input end, which
tapered walls lead to planar, opposing parallel walls extending
away from the tapered walls to a light output end spaced from and
opposite the light input end, a width of the light output end being
greater than a width of the light input end.
2. The linear illumination source of claim 1, wherein said linear
light source is a tubular fluorescent lamp.
3. A linear illumination source of claim 2, wherein
(0.1)(w.sub.1).ltoreq.w.sub.3.ltoreq.w.sub.1.
4. A linear illumination source of claim 2, wherein
(0.2)(w.sub.1).ltoreq.w.sub.3.ltoreq.(0.9)(w.sub.1).
5. The linear illumination source of claim 1, wherein said linear
light source is an array of light emitting diodes, an array of
laser diodes, at least one organic light emitting diode, or at
least one electroluminescent strip.
6. A linear light source of claim 5, wherein the linear light
source is comprised of light emitters of more than one color.
7. The linear illumination source of claim 1, wherein the
reflective material of said external reflective enclosure has a
reflectivity R>90%.
8. The linear illumination source of claim 1, wherein the
reflective material of said external reflective enclosure has a
reflectivity R>95%.
9. A reflective material of claim 8, wherein the reflective
material of said external reflective enclosure is either a diffuse
reflector, a specular reflector, or a combination of diffuse and
specular reflectors.
10. A reflective material of claim 8, wherein the reflecting
material is used as the structural material of said external
reflective enclosure.
11. A reflective material of claim 10 comprising an engineering
thermoplastic filled with fine particles of a clear or white filler
wherein the index of refraction of said fine particles is greater
than the index of refraction of said thermoplastic.
12. The linear illumination source of claim 1, wherein said linear
opening has a width that varies along the length of the
illumination source.
13. A linear illumination system of claim 1, wherein said optical
element is a waveguide or a light pipe.
14. A linear illumination system of claim 1, wherein said linear
opening has a maximum width w.sub.3 such that
(0.05)(w2).ltoreq.w.sub.3.ltoreq.(0.50)(w.sub.2).
15. A linear illumination system of claim 1, wherein said linear
light source is a tubular fluorescent lamp.
16. A linear illumination system of claim 15, wherein
(0.1)(w.sub.1).ltoreq.w.sub.3.ltoreq.(1.0)(w.sub.1).
17. A linear illumination system of claim 15, wherein
(0.2)(w.sub.1).ltoreq.w.sub.3.ltoreq.(0.9)(w.sub.1).
18. The linear illumination source of claim 1 wherein the external
reflective enclosure has a circular cross sectional shape.
19. The linear illumination source of claim 1 wherein the external
reflective enclosure comprises a structural support.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention generally relates to high-efficiency, linear
illumination sources and linear illumination systems which have
enhanced output irradiance and radiance. Irradiance is defined as
the light flux per unit area and can be expressed, for example, in
units of watts per square centimeter (W/cm.sup.2). Radiance is the
brightness of the light. Radiance can be expressed, for example, in
units of watts per square centimeter per steradian
(W/(cm.sup.2.multidot.steradian), where a steradian is the unit of
solid angle.
For many applications, an illumination source with a narrow output
opening and high output efficiency is preferred. Such a source is
commonly constructed using an aperture lamp with an internal slit
aperture built into the lamp structure. However, an aperture lamp
generally has lower light emission than a conventional lamp due to
increased light absorption inside the lamp and due to a reduction
in the surface area of the phosphor coating. It would be highly
desirable to have an improved narrow illumination source that is
more efficient than a lamp with an internal slit aperture.
For applications such as, for example, optical scanners and
photocopiers, a linear illumination system with high output
irradiance is desired in order to illuminate a narrow strip of the
area being scanned or photocopied. The illumination assembly for
such a device commonly consists of a bare linear light source, an
aperture lamp, or a lamp partially surrounded with a specular
reflector. A specular reflector is a mirror-like reflector with a
smooth surface and has the property that the angle of light
incidence equals the angle of reflection, where the incident and
reflection angles are measured relative to the direction normal to
the surface. An improved linear illumination system which has
higher output irradiance would be advantageous.
For certain other applications such as flat panel displays, an
illumination system having a very shallow thickness is highly
desirable. Such systems are commonly configured with one or more
illumination sources, a waveguide or light pipe for collecting and
distributing the light from the illumination sources, and
additional scattering, reflecting, or collimating elements for
extracting the light from the waveguide. A significant depth
savings can be achieved by coupling the illumination sources
through the edge of the waveguide. The amount of light extracted
from the system is proportional to the number of reflections or
scattering events that occur within the waveguide, the number being
inversely proportional to the thickness of the waveguide. To obtain
maximum light output, a thin waveguide is preferable. However, this
results in waveguide edges having a small surface area, limiting
the size of the illumination source that can directly adjoin the
edge of the waveguide. On the other hand, if the surface area of
the waveguide edge is increased, the extraction efficiency of the
waveguide will decrease. It would be highly desirable to utilize a
thin waveguide yet provide the maximum illumination source input.
Therefore, a highly-efficient, linear illumination source with high
output irradiance and radiance from a narrow opening is needed.
2. Description of the Prior Art
It is well-known that it is possible to use tubular fluorescent
lamps having an internal slit aperture in order to concentrate and
direct the emitted light into a narrow angular range. Two types of
aperture lamps with internal slits are in general use. The first
type is shown in cross section as aperture lamp 10 in FIG. 1. The
lamp is composed of a hollow glass tube 12 having a phosphor
coating 14 on the entire inside surface except in one narrow region
16 subtending angle 18. The center of the tube is filled with a
mixture of gases which, when excited by an electric current
supplied by electrodes (not shown) at the ends of the tube, emits
ultraviolet light. The ultraviolet light, in turn, strikes the
phosphor coating 14 and is converted to visible light. A typical
phosphor coating is also a diffuse reflector. Note that a diffuse
reflector is a reflector that scatters incident light into a range
of angles. Diffuse reflectors typically have high reflectivity only
when the reflective coating is relatively thick (e.g. about 0.15 mm
or greater). The reflective phosphor coating on the inside of an
aperture lamp is, by necessity, significantly thinner than 0.15 mm
resulting in poor reflectivity (on the order of 60-80%). Most of
the light not reflected by the phosphor is transmitted through the
coating. By placing an aperture, in this case gap 16, in the
phosphor coating, light can be directed preferentially out the
aperture. However, due to loss of some of the light through the
phosphor coating, the effectiveness of this type of aperture lamp
is significantly reduced.
A second type of lamp having an internal aperture and known to
those skilled in the art is shown in FIG. 2 as aperture lamp 50.
The lamp has a glass tube 52. Inside the glass tube is a phosphor
coating 54 and an additional reflective coating 56. There is
an-aperture opening 58 through both the phosphor coating 54 and
reflective coating 56 which subtends angle 59 and which allows
light to escape preferentially in one direction.
There are six significant problems associated with the internal
aperture lamps 10 and 50 shown in FIGS. 1 and 2. First, the
phosphor and reflective coatings must be very thin and the
selection of coating materials is very limited so as not to
interfere with the operation of the lamp. No organic materials are
possible for an internal coating because any outgassing from the
organic material or decomposition of the organic material from the
effects of ultraviolet light would lower the efficiency of the
lamp. Second, because of the restrictions on coating materials, the
reflectivity of the coatings is not as high as desired. Third, a
significant amount of ultraviolet light generated inside the lamp
is wasted due to absorption by the glass tube in the area without
the phosphor coating. Fourth, a more expensive glass must be used
to make these types of aperture lamps in order to reduce
ultraviolet light induced discoloration and loss of light
transmission of the glass in the area of the aperture. Fifth,
because the area of the internal lamp surface which is covered by
the phosphor coating is reduced by the area which includes the
aperture, there is a corresponding reduction in the efficiency of
converting electrical power to light energy. Sixth, internal
aperture lamps are more difficult to manufacture than conventional
lamps and therefore are more expensive. Such deficiencies
contribute to reduced efficiency and higher costs for aperture
lamps compared to regular lamps without internal apertures.
Accordingly, there are now provided with this invention improved
linear illumination sources which utilize external, highly
reflective enclosures incorporating one or more linear openings in
order to achieve improved source efficiency, output irradiance and
output radiance. Such improved illumination sources may be combined
with additional optical elements to produce more complex
illumination systems. Additional objects of the present invention
will become apparent from the following description.
SUMMARY OF THE INVENTION
One embodiment of the present invention is an improved linear
illumination source. The linear illumination source comprises: (a)
a linear light source having a width w.sub.1 in a direction
perpendicular to the long axis of the linear source, and (b) a
external reflective enclosure partially surrounding the
aforementioned linear light source, wherein the external reflective
enclosure has a maximum inside width w.sub.2, and wherein the
external reflective enclosure has at least one linear opening of
maximum width w.sub.3 such that
(0.03)(w.sub.2).ltoreq.w.sub.3.ltoreq.(0.75)(w.sub.2). A linear
light source is defined as a light source having a length dimension
that is at least three times the width dimension w.sub.1. A linear
light source may be comprised of a single element or may be a
linear array containing a multiplicity of elements. If the linear
light source is an array containing a multiplicity of elements,
then the length of the array is at least three times the width of
an individual element. A linear opening is defined as an opening
having a length dimension that is at least three times the width
dimension.
Another embodiment of the invention is disclosed which is directed
to a linear illumination system which utilizes the aforementioned
linear illumination source and one or more additional optical
elements in order to achieve a system with high optical efficiency
and high output irradiance and/or radiance. Such a linear
illumination system comprises: (a) a linear light source having a
width w.sub.1 in a direction perpendicular to the long axis of the
linear source, (b) an external reflective enclosure partially
surrounding the aforementioned linear light source, wherein the
external reflective enclosure has a maximum inside width w.sub.2,
and wherein the external reflective enclosure has at least one
linear opening of maximum width w.sub.3 such that
(0.03)(w.sub.2).ltoreq.W.sub.3.ltoreq.(0.75)(w.sub.2), and (c) at
least one optical element in close proximity to at least one linear
opening. An optical element may include, for example, a cylindrical
rod lens, a lenticular lens, an aspherical lenticular lens, a
lenticular prism, an array of lenticular lenses, an array of
lenticular prisms, a mirror, a reflecting concentrator, or a
waveguide. By lenticular, we mean a linear optical element having
the cross-section (in one direction only) of a lens or a prism.
The embodiments of the present invention will be better understood
by reference to the following detailed discussions of specific
embodiments and the attached figures which illustrate and exemplify
such embodiments.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be more fully understood and further advantages
will become apparent when reference is made to the following
detailed description of the invention and the accompanying drawings
in which:
FIG. 1 is a schematic cross-sectional diagram of an internal
aperture lamp of the prior art;
FIG. 2 is a schematic cross-sectional diagram of an alternative
internal aperture lamp of the prior art;
FIG. 3 is a schematic cross-sectional diagram of a linear
illumination source;
FIGS. 4 and 5 are respectively, schematic cross-sectional and
perspective diagrams of an alternative version of a linear
illumination source;
FIGS. 6 and 7 are respectively, schematic cross-sectional and
perspective diagrams of another version of a linear illumination
source;
FIG. 8 is a schematic cross-sectional diagram of another linear
illumination source;
FIG. 9 is a schematic cross-sectional diagram of a linear
illumination system utilizing the linear illumination source of
FIG. 4 and a waveguide;
FIGS. 10 and 11 are, respectively, schematic cross-sectional and
perspective diagrams of a linear illumination system utilizing the
linear illumination source of FIG. 4 and a lens;
FIG. 12 is a schematic cross-sectional diagram of a linear
illumination system utilizing the linear illumination source of
FIG. 4 and a lens that functions both by refraction and total
internal reflection;
FIG. 13 is a schematic cross-sectional diagram of a linear
illumination system utilizing the linear illumination source of
FIG. 4 and a compound parabolic concentrator (CPC); and
FIG. 14 is a schematic cross-sectional diagram of a linear
illumination system utilizing the linear illumination source of
FIG. 4 and an array of optical elements.
FIG. 15 is a plot of intensity (irradiance) versus detector
position.
FIG. 16 is a plot of intensity (irradiance) versus detector
position.
FIG. 17 is a plot of relative output versus opening width.
FIG. 18 is a plot of intensity (irradiance) versus detector
position.
FIG. 19 shows a linear opening which varies in width along the
length of the illumination source.
DESCRIPTION OF THE INVENTION
The following preferred embodiments as exemplified by the drawings
are illustrative of the invention and are not intended to limit the
scope of the invention as encompassed by the claims of this
application. Illumination sources and illumination systems using
improved external reflective enclosures, linear openings and,
optionally, additional optical elements are disclosed herein.
One embodiment of this invention is a linear illumination source
100 shown in cross-section in FIG. 3. Linear illumination source
100 is comprised of linear light source 102 that is partially
surrounded by an external enclosure 104. The linear light source
102 may be centered in the external enclosure 104 or displaced to
one side of the enclosure. One or more linear openings 108 in the
wall of the external enclosure allow light to escape from the
enclosure. In close proximity to the inside surface of the external
enclosure 104 is a reflective layer 106. In this figure, the width
of the linear light source is 110, the maximum inside width of the
external enclosure is 112, and the maximum width of the linear
opening is 114. Optionally, if the external enclosure 104 is
constructed from a transparent material, the external enclosure may
completely surround the linear light source 102. However, an
opening 108 must still remain in the reflective layer 106 in order
for light to escape from the linear illumination source.
The linear light source 102 can be any source that emits light.
Exemplary linear light sources include, but are not limited to, one
or more of the following types of light sources: fluorescent lamps,
light emitting diodes (LEDs), laser diodes, organic light emitting
diodes, electroluminescent strips, or high-intensity discharge
lamps. As an illustrative example, a multiplicity of light emitting
diodes placed in a row is a linear light source. The single or
multiple elements of the linear light source may emit light of one
color, multiple colors, or white light (which is composed of
multiple colors). The linear light source 102 illustrated in FIG. 3
can emit light in all directions. A. fluorescent lamp is an example
of a linear light source 102 that emits light in all directions. In
order to maximize the efficiency of the linear illumination system
100, it is preferable that linear light source 102 have a
non-absorptive surface 116. Such a non-absorptive surface 116 may
be reflective, transmissive or both.
There is a gap 118 between the surface 116 of the linear light
source 102 and the reflective layer 106. Having a gap between
linear light source 102 and the reflective layer 106 is critical if
the linear light source 102 is a fluorescent lamp or other type of
lamp where the magnitude of the light output of the lamp is
sensitive to the lamp temperature. The gap 118 can act as an
insulating layer which will allow the linear light source 102 to
warm up quickly to its optimum operating temperature. Preferably
the gap is greater than about 10% of the width 110 of the linear
light source.
The external enclosure 104 shown in FIG. 3 can have any
cross-sectional shape including, but not limited to, circular,
elliptical, oval, cusp-shaped, or faceted. The linear opening 108
preferably has a maximum width 114 that is less than the maximum
inside width 112 of the external enclosure 104. More preferably,
the maximum width 114 of linear opening 108 ranges from about 3% to
about 75% of the maximum inside width 112 of the external
enclosure. Most preferably, the maximum width 114 of linear opening
108 ranges from about 5% to about 50% of the maximum inside width
112 of the external enclosure. In addition, if linear light source
102 is a tubular fluorescent lamp, preferably the maximum width 114
of linear opening 108 ranges from about 10% to about 100% of the
width 110 of the linear light source. More preferably, the width
114 of the linear opening 108 ranges from about 20% to about 90% of
the width 110 of the linear light source. The width of the linear
opening 108 may be uniform along the length of the linear light
source or the width of linear opening 108 may vary along the length
of the linear light source in order to change the output light
distribution along the light source. This latter feature of the
current invention provides a critical advantage for applications
requiring a uniform illumination, whereby the non-uniformity
inherent in the light output of the lamp can be corrected to give a
uniform irradiance. The width of the aperture can be widened at any
point along the length of the lamp where the lamp output is low in
order to provide a relatively constant and uniform output from the
illumination source.
The reflective layer 106 may be constructed from any material that
reflects fight. The reflective layer may be a diffuse reflector, a
specular reflector, or a combination of specular and diffuse
reflectors.
Diffuse reflectors can be made that have very high reflectivities
(for example, greater than 95% or greater than 98%). However,
diffuse reflectors with high reflectivities are generally quite
thick. For example, diffuse reflectors with reflectivities greater
than 98% are typically several millimeters thick. Examples of
diffuse reflectors include, but are not limited to, fluoropolymer
materials such as Spectralon.TM. from Labsphere, Inc. and
polytetrafluoroethylene (PTFE) film from Fluorglas (sold under the
trade name Furon.TM.), W. L. Gore and Associates, Inc. (sold under
the trade name DRP.TM.), or E. I. du Pont de Nemours & Company
(sold under the trade name of Teflon.TM.), films of barium sulfate,
porous polymer films containing tiny air channels such as
polyethersulfone and polypropylene filter materials made by Pall
Gelman Sciences, and polymer composites utilizing reflective filler
materials such as, for example, titanium dioxide. An example of the
latter material is titanium-dioxide-filled ABS
(acrylonitrile-butadiene-styrene terpolymer) produced by RTP. In
the case that a structural material is employed as a reflective
material, such as titanium dioxide filled ABS, the structural
support 104 can be combined with the reflective layer 106 as shown
in FIGS. 4 and 5.
Most specular reflective materials have reflectivities ranging from
about 80% to about 93%. Any light that is not reflected by the
specular reflector is absorbed and converted to heat, thus lowering
the efficiency of any optical system utilizing such a reflector.
Examples of specular reflective materials include, but are not
limited to, Silverlux.TM., a product of 3M, and other carrier films
of plastic which have been coated with a thin metallic layer such
as silver, aluminum or gold. The thickness of the metallic coating
may range from about 0.05 .mu.m to about 0.1 mm, depending on the
materials used and the method of manufacturing the metal
coating.
An example of a combination of specular and diffuse reflective
materials is one or more layers of a diffuse reflector that is
backed by a specular reflector. Such a combination of specular and
diffuse reflective materials is disclosed in U.S. patent
application Ser. No. 08/679,047 and is incorporated herein by
reference. The use of a combination of specular and diffuse
reflective materials may result in higher reflectivity in a thinner
layer than is possible using a diffuse reflective material
alone.
The efficiency of illumination source 100 can be defined as the
percentage of the light emitted from linear light source 102 that
escapes through linear opening 108. The efficiency depends strongly
on the width 114 of linear a opening 108, the circumference of the
inside surface of reflective layer 106, the reflectivity of the
reflective layer 106 and the reflectivity of the linear light
source 102. For example, if the width 114 of linear opening 108 is
1/10 of the circumference of the inside surface of reflective layer
106, then only 10% of the light that is emitted from linear light
source 102 will escape through linear opening 108 without being
reflected by reflective layer 106. The remaining 90% of the light
will be reflected one or more times by reflective layer 106 or by
the linear light source 102 before escaping from linear opening 108
or before being absorbed by the reflective surfaces and converted
to heat. Some of the light may be reflected ten times or more
before escaping. The large number of times that the light can be
reflected makes it very important that the reflectivity of the
reflecting layer 106 be as close to 100% as the practical
considerations of space and cost will allow. For example, if the
reflectivity of an optical surface is 90% per reflection and the
light reflects ten times from that surface, the overall efficiency
is (0.90).sup.10 or 35%. The other 65% of the light is lost.
However, if the reflectivity of the reflector is increased to 95%
per reflection and the light reflects ten times from that surface,
the overall efficiency is (0.95).sup.10 or 60%, a significant
improvement over 35%. Greater improvements may be attained if the
reflectivity is greater than 95%. Thus, for the present invention,
the reflectivity of the material employed for layer 106 is
preferably greater than 90%, more preferably greater than 95%, and
most preferably greater than about 97%.
Another embodiment of this invention is shown as linear
illumination source 150 in FIG. 4 (a cross-sectional view) and in
FIG. 5 (a perspective view). In this embodiment, linear light
source 152 having width 160 is partially surrounded by an external
reflective enclosure 154 having a maximum inside width 162. One or
more linear openings 158 in the wall of the external reflective
enclosure 154 allow light to escape from the enclosure. The maximum
width of the linear opening 158 is dimension 164. The external
reflective enclosure 154 shown in FIGS. 4 and 5 can have any
cross-sectional shape including, but not limited to, circular,
elliptical, oval, cusp-shaped, or faceted. The linear opening 158
preferably has a maximum width 164 that is less than the maximum
inside width 162 of the external reflective enclosure 154. More
preferably, the maximum width 164 of linear opening 158 ranges from
about 3% to about 75% of the maximum inside width 162 of the
external reflective enclosure. Most preferably, the maximum width
164 of linear opening 158 ranges from about 5% to about 50% of the
maximum inside width 162 of the external reflective enclosure. In
addition, if linear light source 152 is a tubular fluorescent lamp,
preferably the maximum width 164 of linear opening 158 ranges from
about 10% to about 100% of the width 160 of the linear light
source. More preferably, the width 164 of the linear opening 158
ranges from about 20% to about 90% of the width 160 of the linear
light source. The width of the linear opening 158 may be uniform
along the length of the linear light source or the width of linear
opening 158 may vary along the length of the linear light source in
order to change the output light distribution along the light
source to compensate for non-uniformities in the light source as
shown in FIG. 19.
The embodiment shown in FIGS. 4 and 5 is similar to FIG. 3 except
that now the structural material of the external enclosure 154 is
also the reflective material. This embodiment is especially useful
if the structural material for the external reflective enclosure is
a diffuse reflector. Examples of diffuse reflectors are listed
above. Preferably the reflective material can be cut, formed,
extruded, or molded into the required shape for the external
reflective enclosure and, of course, possesses sufficient tensile
modulus, flexual modulus, heat deflection temperature, and impact
resistance to serve as the structural member for the illumination
system.
Preferred reflective materials for use in the particular
embodiments 150, 200, 300, 350, 400, 450, and 500 are engineering
thermoplastics which have been filled with fine particles which
have an index of refraction which is substantially greater than
that of the host polymer and are optically clear or white in their
neat form, such as titanium dioxide (rutile and anatase), aluminum
oxide, zinc oxide, zinc sulfide, barium sulfate, antimony oxide,
magnesium oxide, calcium carbonate, strontium titantate, and the
like. Preferred materials also include engineering thermoplastics
which contain particles, voids or gas-filled bubbles created, for
example, by foaming, and whereby the particles, voids or bubbles
possess an index of refraction substantially less than that of the
host polymer. Although the primary particle size can be much finer,
as dispersed in the polymer matrix, the filler particles or voids
preferably lie in the size range from about 0.1 microns to about
3.0 microns and most preferably from about 0.1 microns to about 1
microns. The optimal size of a filler particle may be predicted
from the relation d=2.lambda..sub.o /(.pi.n.delta.), where d is the
diameter of the particle, .lambda..sub.o is the vacuum wavelength
of interest, n is the index of refraction of the matrix polymer and
.delta. is the difference in the indices of refraction of the
filler and the matrix. Thermoplastics useful in this invention are
preferably non-yellow and include a wide variety of plastics known
in the art to be useful for injection molding or extrusion, such
as, for example, ABS, poly (methyl methacrylate) poly(ethylene
terephthalate) (PET), poly(butylene terephthalate) (PBT),
polypropylene, nylon 6, nylon 66, polycarbonate, polystyrene,
poly(phenylene oxide), and blends and alloys thereof.
Another embodiment of this invention is shown as linear
illumination source 200 in FIG. 6 (a cross-sectional view) and FIG.
7 (a perspective view). In this embodiment, the linear light source
202 having width 210 is embedded into the side of the external
reflective enclosure 204 which has a maximum inside width 212. One
or more linear openings 208 in the wall of the external reflective
enclosure 204 allow light to escape from the enclosure. The maximum
width of each linear opening 208 is dimension 214. In FIGS. 6 and
7, the linear opening 208 is illustrated to be on the side of the
external reflective enclosure 204 opposite the linear light source
202. However, this is not required and the linear light source 202
and the linear opening 208 may be adjacent to each other. The
external reflective enclosure 206 may be constructed from a diffuse
reflective material or an additional reflective layer may be placed
on the inner surface 206 of external reflective enclosure 204 in
order to achieve high reflectivity. The linear light source 202
illustrated in FIGS. 6 and 7 preferably emits light into a
hemisphere (a solid angle of 2.pi.) or into a solid angle less than
2.pi. and preferably does not emit light in all directions (which
would be a solid angle of 4.pi.). Examples of linear light source
202 include, but are not limited to, light emitting diodes, laser
diodes, organic light emitting diodes, and electroluminescent
strips. In this embodiment of the invention, the external
reflective enclosure 204 can also serve to homogenize the light
output from the linear light source 202. This homogenization is
especially important if the linear light source 202 is an array of
light emitting diodes, laser diodes, or organic light emitting
diodes, each of which may have a very small light emitting surface.
If the linear light source 202 includes elements that emit
different colors (for example, red, green and blue light emitting
diodes), the external reflective enclosure 204 can mix the colors
to form a white light output.
Another embodiment of this invention is illustrated by the linear
illumination source 250 shown in cross-section in FIG. 8. This
configuration is especially useful if the linear light source is,
for example, a tubular fluorescent lamp which is illustrated in
FIG. 8 as a transparent glass envelope 252 that is coated on the
inside with a phosphor layer 254. The linear light source is
surrounded by external enclosure 256 except for opening 264 having
an opening width 262. The external enclosure 256 may be constructed
from a reflective material, a non-reflective material, or a
transparent material. If the external enclosure is constructed from
a non-reflective or transparent material, an additional reflective
layer 258 is needed on the inside surface of external enclosure
256. The reflective structure or structures, including external
enclosure 256 and/or reflecting layer 258, may be constructed from
diffuse reflective materials, specular reflective materials, or a
combination of diffuse reflective materials and specular reflective
materials. Examples of diffuse and specular reflective materials
are listed above. FIG. 8 is similar to FIG. 3 except that in FIG. 8
there is little or no gap between the linear light source and the
reflecting layer 258. In the preferred embodiment, the gap is less
than 10% of the lamp width 260. If the linear light source is a
fluorescent lamp, removing the gap can lead to higher output
efficiency of the linear illumination source by decreasing the
number of times the light must reflect inside the external
reflective enclosure before is escapes from opening 264. (Note that
the phosphor coating inside a fluorescent lamp typically has a
reflectivity of approximately 60-80% with most of the remainder of
the light being transmitted so that it is possible for light to
travel from one side of the lamp to the other by passing through
the phosphor coating.) However, fluorescent lamps are very
sensitive to the temperature of their surroundings. Placing the
external enclosure 256 and/or the reflective layer 258 in close
proximity or actual contact with the fluorescent lamp may lengthen
the warm-up time of the lamp with resulting reduced light output
while the lamp is warming up, or may lower the steady-state
operating temperature of the fluorescent lamp which again could
result in lower light output. Optionally, if the external enclosure
256 is constructed from a transparent material and a reflective
layer 258 is utilized, the external enclosure 256 may completely
surround the glass envelope 252 of the fluorescent lamp. However,
an opening 264 must still remain in reflective layer 258 in order
for light to escape from the linear illumination source. An example
of the optional configuration would be to use a flexible, diffuse,
reflective layer 258 having an opening 264 and to use transparent
shrink tubing for the external enclosure 256. After the pieces are
assembled into the correct configuration, the shrink tubing can be
heated causing it to shrink tightly around the reflector and
fluorescent lamp.
Other embodiments of this invention involve using linear
illumination sources of the type illustrated in FIGS. 3-8 to make
more complex linear illumination systems. The linear illumination
systems may include additional optical elements such as, for
example, waveguides, cylindrical rod lenses, lenticular lenses,
aspherical lenticular lenses, arrays of lenticular lenses, prisms,
arrays of lenticular prisms, reflectors, concentrators and
collimators. The optical elements may be used to shape, focus,
collimate, or project the light being emitted from the linear
illumination source. Examples of such illumination systems are
illustrated in FIGS. 9-14 and are not meant to limit the scope of
this invention. Note, for example, that any of the linear
illumination sources illustrated in FIGS. 3-8 may be used with any
of the optical elements in order to make additional linear
illumination systems. Likewise, the additional optical elements may
also be used in combination, such as the lens of FIG. 10 together
with the light guide of FIG. 9, or a lens and CPC can be integrated
together, or multi-stage CPC's in series may be employed.
The diagram in FIG. 9 illustrates another embodiment of this
invention. Linear illumination system 300 is comprised of a linear
illumination source 320 and optical waveguide 316. By way of
example, linear illumination source 320 is illustrated to be of the
type shown previously in FIG. 4 and is further comprised of a
linear light source 302 and a external reflective enclosure 304. A
linear opening 308 in external reflective enclosure 304 allows
light to pass from the linear illumination source 320 to an optical
waveguide 316. The optical waveguide may be used to transport the
light by total internal reflection (TIR) to places remote from the
linear illumination source 320. As will be understood by those
skilled in the art, other optical components may be used with
optical waveguide 316 to form additional illumination systems.
Applications for such linear illumination systems include edge-lit
illumination systems for flat panel displays and collimating
illumination systems.
Illustrated in FIG. 10 (a cross-sectional view) and FIG. 11 (a
perspective view) is another embodiment of this invention. Linear
illumination system 350 is comprised of linear illumination source
370 and a lens 366. By way of example, linear illumination source
370 is illustrated to be of the type shown previously in FIG. 4. A
linear opening 358 in the external reflective enclosure 354 allows
light to pass from the linear illumination source 370 to the lens
366. In order to achieve higher output irradiance and radiance for
the linear illumination system, preferably linear opening 358 has a
maximum width 364 that is less than the maximum inside width 362 of
the external reflective enclosure 354. More preferably, the maximum
width 364 of the linear opening 358 ranges from about 3% to about
75% of the maximum inside width 362 of the external reflective
enclosure. Most preferably, the maximum width 364 of linear opening
358 ranges from about 5% to about 50% of the maximum inside width
362 of the external reflective enclosure. In addition, if linear
light source 352 is a tubular fluorescent lamp, preferably the
maximum width 364 of the linear opening 358 ranges from about 5% to
about 100% of the width 360 of the linear light source 352. More
preferably, the width 364 of the linear opening 358 ranges from
about 20% to about 90% of the width 360 of the linear light source.
Examples of lens 366 include, but are not limited to, a lenticular
lens, an aspherical lenticular lens, a cylindrical rod lens, a
plano-convex lenticular lens, a double-convex lenticular lens, a
lenticular Fresnel lens, and multi-element lenses of any type.
Especially useful are linear illumination systems in which the lens
366 is a cylindrical rod lens as is illustrated in FIGS. 10 and 11.
Lens 366 may be constructed from any transparent material. Linear
illumination systems may be used in many applications including,
for example, optical scanners, facsimile machines, and
photocopiers.
FIG. 12 illustrates another embodiment of this invention. Linear
illumination system 400 is comprised of linear illumination source
430 and a transparent optical element 416. By way of example, the
linear illumination source 430 is illustrated to be of the type
shown in FIG. 4 and is, in turn, comprised of linear fight source
402 and external reflective enclosure 404. External reflective
enclosure 404 has a linear opening 408 with a maximum width 414
that allows light to pass from the linear illumination source 430
to the transparent optical element 416. Transparent optical element
416 has an input surface 418 adjacent to opening 408, a tapered
section of length 432 bounded by sidewalls 420 and 422, and an
output surface 424. Optionally, transparent optical element 416
also includes a straight section with parallel sidewalls 434 and
436, whereby the straight section is positioned between the tapered
section (bounded by the sidewalls 420 and 422) and the output
surface 424. Preferably the input surface 418 is planar but
planarity is not required. The output width 428 of the optical
element 416 is preferably greater than the input width 426 of the
tapered section. More preferably, the output width 428 of the
optical element 416 is at least two times the input width 426. The
sidewalls 420 and 422 of the tapered section may be planar, curved,
or faceted. The output surface 424 of the transparent optical
element 416 may also be planar, curved, or faceted. Preferably the
output surface 424 is a curved lenticular lens, whereby the lens
may have a single radius of curvature, may be parabolic in shape,
or may have some general shape having no single radius of
curvature. More preferably, output surface 424 has a single radius
of curvature R, where the radius of curvature R may range from
one-half of the output width 428 to about 1.5 times one-half of the
output width 428. In other words, the range of the radius of
curvature R is
Light enters transparent optical element 416 through input surface
418. Some of the light undergoes reflections from the inner
surfaces of sidewalls 420 and 422 and from the inner surfaces of
the optional sidewalls 434 and 436. The reflections may occur by
TIR if the sidewalls 420, 422, 434, and 436 are uncoated or may
occur by normal reflection if the sidewalls are coated with a
reflective coating. Since the sidewalls 420 and 422 form an
expanding taper, the light will be partially collimated by the
tapered section of the optical element 416. The light then exits
through the output surface 424 which can further shape the output
light beam. Output surface 424 may result in a light output beam
that is either more collimated or more focused.
FIG. 13 illustrates another embodiment of this invention. Linear
illumination system 450 is comprised of an illumination source 476
and a tapered optical structure 466. By way of example, linear
illumination source 476 is illustrated to be of the type shown in
FIG. 4. The illumination source 476 is further comprised of a
linear light source 452 and an external reflective enclosure 454.
An opening 458 in the external reflective enclosure 454 allows
light to pass from the illumination source 452 to the tapered
optical structure 466 having sidewalls 470 and 472. If the tapered
optical structure 466 is a solid structure (not hollow), preferably
the light input end 468 of tapered optical structure 466 is a
planar surface, but planarity is not required. The output width 480
of tapered optical structure 466 is greater than the input width
478. Preferably, the output width 480 of the tapered optical
structure 466 is at least two times the input width 478. Especially
useful are linear illumination systems in which the sidewalls 470
and 472 of the tapered optical waveguide have a parabolic shape or
the shape of a compound parabolic concentrator (CPC). The tapered
optical structure 466 may be constructed from a solid transparent
material having surfaces 470 and 472 that are either uncoated or
coated with a reflective material or the tapered optical structure
466 may be a hollow structure with surfaces 470 and 472 coated with
a reflective material and with open ends 468 and 474. Light enters
the tapered optical structure 466 at input end 468, reflects from
surfaces 470 and 472 and exits at output end 474. As a result of
the tapered sides of the optical structure 466, the light at the
output end 474 of the taper is more collimated than the light at
the input end 468. In the case that the optical structure 466 is
fabricated from a clear dielectric material, it is also possible to
make the output end 474 not planar as shown but convex. In such a
case, a given degree of collimation can be achieved with an element
of shorter length, where length is defined as the perpendicular
distance from input end 468 to the output end 474.
Another embodiment of this invention is illustrated in FIG. 14 as
linear illumination system 500. Linear illumination system 500 is
comprised of linear illumination source 520 and an array 516 of
lenticular optical elements 518. By way of example, linear
illumination source 520 is illustrated to be of the type shown in
FIG. 4. Linear illumination source 520 is further comprised of
linear light source 502 which is partially surrounded by external
reflective enclosure 504 with opening 508. The lenticular optical
elements 518 may include lenticular prisms and lenticular lenses
used separately or in combination. If the lenticular optical
elements 518 are lenticular prisms, the sidewalls of the prisms may
be planar, curved or faceted. If the lenticular optical elements
518 are lenticular lenses, the lenses may have one radius of
curvature, multiple radii of curvature, or may be aspherical
lenticular lenses. The purpose of the array 516 of lenticular
optical elements is to further shape or collimate or focus the
light emerging from opening 508.
The following examples are included to illustrate some embodiments
of this invention but are not meant to limit the scope of the
invention.
EXAMPLE 1
This example illustrates forming a reflector using a combination of
a layer of diffuse reflective material and a layer of specular
reflective material. Reflectivity measurements were done using a
commercially available Macbeth #3100 Spectrophotometer. The
reflectivity of a 0.5 mm (0.020 inch) thick sheet of white,
diffuse, polytetrafluoroethylene material (product number 128-10
white) produced by Furon, Hoosick Falls, N.Y., was measured and
found to be 95.6% with no specular reflector backing. When a
specular reflective sheet of Silverlux.TM. (3M) having a
reflectance of 92% was placed on the back side of the white diffuse
material, the reflectivity of the composite material increased to
96.8%, a number that is larger than either of the two reflective
sheets measured separately. Increases in reflectivity of this
magnitude are quite important for illumination systems in which
light is reflected many times inside the system. For example, if
light is reflected twenty times inside the illumination system, the
overall efficiency of the twenty reflections would be
(0.956).sup.20 or 40.7% for the diffuse reflective material used
alone, (0.920).sup.20 or 18.9% for the specular reflective material
used alone, and (0.968).sup.20 or 52.2% for the combination of
reflective materials. In this example, the combination of diffuse
and specular reflective materials is 28% more efficient than the
diffuse reflective material used alone and 176% more efficient than
the specular reflective material used alone.
EXAMPLE 2
In this example, the efficiency of a commercially available
fluorescent aperture lamp having an internal aperture (utilizing
the prior art configuration shown schematically in FIG. 2) was
compared to an improved illumination source design as described in
this invention.
The commercially available internal aperture lamp was a 3 mm
diameter cold-cathode fluorescent lamp made by LCD Lighting. This
lamp had a 90.degree. internal aperture which allowed light to
escape predominantly from one side of the lamp. Note that a
90.degree. aperture corresponds to the case where the width of the
aperture is approximately 50% of the internal width of the
reflecting layer. The lamp was placed inside an integrating sphere
and the total light output was measured. Dividing the total light
output by the length of the lamp resulted in an output-per unit
length of 4.0 lumens/inch.
A second lamp (the same length as the preceding aperture lamp) was
obtained from LCD Lighting having no internal aperture but having
the same technical characteristics (3 mm diameter and the same
phosphor and gas fill compositions) as the preceding aperture lamp.
This lamp was tightly wrapped with a combination of diffuse and
specular reflective materials except for a linear opening of
90.degree. which allowed the light to escape. In this case, the
combination of diffuse and specular reflective materials was on the
outside of the glass envelope of the lamp forming a linear external
opening. The combination of diffuse and specular reflective
materials was made up of a 0.25 mm (0.010 inch) thick sheet of
Furon.TM., a polytetrafluoroethylene diffuse reflective material
purchased from Fluorglas, and was backed by a layer of
Silverlux.TM. specular reflective material purchased from 3M. The
reflecting materials were held in place by completely surrounding
the lamp and the reflective materials with a transparent plastic
shrink tube and then heating the shrink tube until it tightly
compressed the reflecting materials onto the outside surface of the
lamp. The illumination source was placed inside an integrating
sphere and the total light output was measured. Dividing by the
length of the lamp to convert to lumens/inch resulted in an output
of 6.8 lumens/inch which is a 70% improvement in efficiency over
the internal aperture lamp.
EXAMPLE 3
The two illumination sources of Example 2, the internal 90.degree.
aperture lamp from LCD Lighting and the improved linear
illumination source of this invention, were each used to illuminate
a surface 4 mm from the lamps. The irradiance (in units of
mW/cm.sup.2) was measured for both sources. At the 4 mm distance,
the irradiance from the standard internal aperture lamp was 3.4
mW/cm.sup.2. The irradiance from the improved illumination source
of this invention was 5.6 mW/cm.sup.2, an improvement of 65%.
EXAMPLE 4
A linear illumination source was constructed utilizing the
configuration shown schematically in FIG. 4 and was compared to a
linear illumination system that was constructed utilizing the
configuration shown schematically in FIG. 10 and that includes an
external lens. For both cases, the light source was a cold-cathode
fluorescent lamp made by Harrison that had an outside diameter of
2.6 mm and a length of 268 mm. The lamp was driven by an inverter
using an inverter input power of approximately 3.7 watts. The light
output of the bare lamp was-measured using a calibrated integrating
sphere and found to be 123 lumens. A external reflective enclosure
surrounded the lamp except for a linear opening whose width could
be adjusted. The external reflective enclosure was constructed from
two pieces of Spectralon.TM. (from Labsphere Inc.). Spectralon.TM.
is a diffuse reflecting solid whose reflectivity depends on the
thickness of the material. For 555 nm light, a section of
Spectralon.TM. that is 3 mm thick has a reflectivity of 97.2%. The
two pieces of reflecting material were machined such that the shape
of the enclosure was oval. The maximum inside width of the oval
enclosure was approximately 7.0 mm and a minimum inside width of
the oval enclosure was approximately 4.6 mm. A linear opening in
one side of the enclosure was adjusted to have a uniform width of
1.15 mm. Note that when the width of the linear opening was 1.15
mm, the opening width is only approximately 16% of the maximum
internal width of the enclosure and approximately 44% of the width
of the lamp. For the case of the linear illumination system, either
a rod lens approximately 3.18 mm in diameter or a plano-convex
cylinder lens was placed outside the enclosure and approximately
3.5 mm from the oval cavity in the external reflective enclosure.
For all three cases (i.e. no lens, a rod lens, or a plano-convex
cylinder lens), the irradiance (in mW/cm.sup.2) of the linear
illumination system was measured at a distance of 7 mm from the rod
lens using a 1 mm diameter detector. Within the 7 mm distance was a
3 mm thick glass plate which simulated the optical arrangement
typically encountered inside a flatbed document scanner. The
detector was moved from side to side over a range of approximately
30 mm to map out the shape of the irradiance distribution
perpendicular to the long axis of the linear illumination system.
The results are shown in FIG. 15. For the linear illumination
source with no lens, the resulting peak irradiance was
approximately 7.3 mW/cm.sup.2. Placing a plano-convex cylinder lens
at the linear opening of the illumination source increased the peak
irradiance to approximately 14 mW/cm.sup.2. Replacing the cylinder
lens with a rod lens resulted in a peak irradiance of approximately
15 mW/cm.sup.2. Utilizing the lens, whether a rod lens or a
plano-convex cylinder lens, greatly improved the peak
irradiance.
EXAMPLE 5
A linear illumination system was constructed utilizing the
configuration shown schematically in FIG. 10 and included a light
source, an external reflective enclosure, and an external lens. The
light source was a cold-cathode fluorescent lamp made by Harrison
that had an outside diameter of 2.6 mm and a length of 268 mm. The
lamp was driven by an inverter using an inverter input power of
approximately 3.7 watts. The light output of the bare lamp was
measured using a calibrated integrating sphere and found to be 123
lumens. A external reflective enclosure surrounded the lamp except
for a linear slit whose width could be adjusted. The external
reflective enclosure was constructed from two pieces of
Spectralon.TM. (from Labsphere Inc.). Spectralon.TM. is a diffuse
reflecting solid whose reflectivity depends on the thickness of the
material. For 555 nm light, a section of Spectralon.TM. that is 3
mm thick has a reflectivity of 97.2%. The two pieces of reflecting
material were machined such that the shape of the enclosure was
oval. The maximum inside width of the oval enclosure was
approximately 7.0 mm and a minimum inside width of the oval
enclosure was approximately 4.6 mm. A linear opening in one side of
the enclosure could be adjusted to have a uniform width ranging
from 1.15 mm to 2.35 mm. Note that when the width of the linear
opening is 2.35 mm, the opening width is less than the width (2.6
mm) of the fluorescent lamp and only approximately 35% of the
maximum inside width of the enclosure. When the width of the linear
opening is 1.15 mm, the opening width is only approximately 16% of
the maximum internal width of the enclosure and approximately 44%
of the width of the lamp. A cylindrical rod lens approximately 3.18
mm in diameter was placed outside the enclosure and approximately
3.5 mm from the oval cavity in the external reflective enclosure.
The irradiance (in mW/cm.sup.2) of the linear illumination system
was measured at a distance of 7 mm from the rod lens using a 1 mm
diameter detector. Within the 7 mm distance was a 3 mm thick glass
plate which simulated the optical arrangement typically encountered
inside a flatbed document scanner. The detector was moved from side
to side over a range of approximately 30 mm to map out the shape of
the irradiance distribution perpendicular to the long axis of the
linear illumination system. The results are shown in FIG. 16. The
narrowest opening width, 1.15 mm, had the highest peak irradiance
(approximately 16 mW/cm.sup.2) but also the narrowest irradiance
distribution (a full width at half maximum of approximately 5 mm).
In contrast, the widest opening width (2.35 mm) had the lowest peak
irradiance (approximately 11.5 mW/cm.sup.2) and the widest
irradiance distribution (a full width at half maximum of
approximately 11 mm). For both the narrowest and widest opening
widths measured, the peak values of irradiance are much higher than
the irradiance of the same linear illumination source without the
lens. The total integrated light output from the linear
illumination system is directly related to the opening width and is
highest for the widest opening as shown in FIG. 17. The normalized
peak irradiance is inversely related to the opening width and is
highest for the smallest opening width (also shown in FIG. 17).
EXAMPLE 6
An experiment was done to measure the output efficiency of a linear
illumination source as a function of the percent reflectivity of
the reflective material. A linear illumination source was
constructed that included a linear light source, an external
tubular enclosure and a layer of reflective material that lined the
inside surface of the external tubular enclosure except for a
linear opening having a fixed width of 1.5 mm. The linear light
source was a cold-cathode fluorescent lamp that had a diameter of
2.6 mm and a length of 268 mm. The lamp was driven by an inverter
using an inverter input power of approximately 3.7 watts. The
external enclosure was constructed from an acrylic tube that had an
inside diameter of 6.4 mm. Five different reflective materials were
placed sequentially inside the enclosure. The materials were:
polyethersulfone filter material (obtained from Pall Gelman
Sciences), Spectraflect.TM. (obtained from Labsphere),
Duraflect.TM. (obtained from Labsphere), Silverlux.TM. (obtained
from 3M), and Predator.TM. (obtained from Pall Gelman Sciences).
All the reflecting materials with the exception of Silverlux.TM.
were diffuse reflectors. The table below shows the resulting
illumination source efficiencies as a function of the material
reflectivity.
Reflecting Material Reflectivity Efficiency Polyethersulfone 97.7%
54.3% Spectraflect .TM. 97.5% 54.3% Duraflect .TM. 96% 48%
Silverlux .TM. 92% 41.9% Predator .TM. 85% 31.3%
Thus, the table demonstrates that small changes in the reflectivity
can result in large changes in the efficiency of the linear
illumination source.
EXAMPLE 7
In this example, two illumination devices utilizing an aperture
lamp were compared to two improved illumination devices as taught
by this invention. Device 1 was a commercially available 3 mm
diameter cold-cathode aperture fluorescent lamp made by LCD
Lighting. This lamp had a 90.degree. internal aperture which
allowed light to escape predominantly from one side of the lamp.
Note that a 90.degree. aperture corresponds to the case where the
width of the aperture is approximately 50% of the internal width of
the reflecting layer. Device 2 used the same aperture lamp as
Device 1 but added a 3.18 mm diameter rod lens placed approximately
3.5 mm from the lamp aperture. For both device 1 and device 2, the
lamp was placed inside a clear acrylic enclosure but no reflective
material was used for the enclosure. Devices 3 and 4 are examples
of embodiments of this invention. Devices 3 and 4 utilized a second
lamp obtained from LCD Lighting having no internal aperture but
having the same technical characteristics (3 mm diameter and the
same phosphor and gas fill compositions) as the preceding aperture
lamp. In addition, for devices 3 and 4, an external reflective
enclosure was placed around the lamp where the external reflective
enclosure had a linear opening whose width was adjusted to 1.15 mm.
The external reflective enclosure was constructed from two pieces
of Spectralon.TM. (from Labsphere Inc.). Spectralon.TM. is a
diffuse reflecting solid whose reflectivity depends on the
thickness of the material. For 555 nm light, a section of
Spectralon.TM. that is 3 mm thick has a reflectivity of 97.2%. The
two pieces of reflecting material were machined such that the shape
of the enclosure was oval. The maximum inside width of the oval
enclosure was approximately 7.0 mm and a minimum inside width of
the oval enclosure was approximately 4.6 mm. For device 4, a rod
lens approximately 3.18 mm in diameter was placed approximately 3.5
mm from the oval cavity in the external reflective enclosure.
Device 3 had no lens. The irradiance (in mW/cm.sup.2) of the linear
illumination system was measured at a distance of 7 mm from the rod
lens using a 1 mm diameter detector. Within the 7 mm distance was a
3 mm thick glass plate which simulated the optical arrangement
typically encountered inside a flatbed document scanner. The
detector was moved from side to side over a range of approximately
30 mm to map out the shape of the irradiance distribution
perpendicular to the long axis of the linear illumination system.
The results are shown in FIG. 18. Device 1 (the aperture lamp
alone) had the worst peak irradiance of about 3.0 mW/cm.sup.2. For
device 2 (the aperture lamp plus the rod lens), the peak irradiance
increased only slightly to 4.29 mW/cm.sup.2. Device 3 (the
non-aperture lamp used with a reflective enclosure taught by this
invention) had a much improved peak irradiance of 7.0 mW/cm.sup.2.
Device 4 (the non-aperture lamp used with a reflective enclosure
and rod lens arrangement taught by this invention) had the highest
peak irradiance of 11.8 mW/cm.sup.2. These results indicated that a
non-aperture lamp used with an external reflecting enclosure having
a narrow linear opening gave a higher directed irradiance than an
internal aperture lamp and that even further improvement in the
directed irradiance was obtained by adding an additional optical
element (in this case, a rod lens).
It should be understood that this invention is applicable to a wide
variety of devices requiring linear illumination sources and linear
illumination systems. Examples include, but are not limited to:
scanners, facsimile machines, photocopiers and direct illumination
devices for commercial, office, residential, outdoor, automotive,
and appliance applications. The inventions herein may also be
applied to displays (e.g. flat panel displays) for computer,
automotive, military, aerospace, consumer, commercial, and
industrial applications.
While there has been described what is believed to be the preferred
embodiments of the invention, those skilled in the art will
recognize that other and further modifications may be made thereto
without departing from the spirit of the invention, and it is
intended to claim all such embodiments that fall within the true
scope of the invention.
* * * * *